Swift 相当于 each_slice

Question

Swift中有没有类似Ruby的Enumerable#each_slice的东西？

ruby 示例:

arr = ["a", "b", "c", "d"]
arr.each_slice(2) {|s1, s2| puts s1 + s2 }

输出:

ab
cd

Answer 1

作为对 How to implement Haskell's splitEvery in Swift? 中代码的小修改, 你可以定义一个数组扩展

extension Array {
    func eachSlice<S>(nInEach: Int, transform: [T] -> S) -> [S] {
        var result = [S]()
        for from in stride(from: 0, to: self.count, by: nInEach) {
            let to = advance(from, nInEach, self.count)
            result.append(transform(Array(self[from ..< to])))
        }
        return result
    }
}

然后将其用作

let arr = ["a", "b", "c", "d"]
arr.eachSlice(2) { println("".join($0)) }

输出:

abcd

Another example:

let iarr = [1, 2, 3, 4, 5, 6, 7]
let sliceSums = iarr.eachSlice(3) {
    reduce($0, 0) { $0 + $1 } // sum of slice elements
}
println(sliceSums)
// [6, 15, 7]

---

Swift 3 更新:

extension Array {
    func eachSlice<S>(_ nInEach: Int, transform: (ArraySlice<Element>) -> S) -> [S] {
        var result = [S]()
        var from = startIndex
        while from != endIndex {
            let to = indices.index(from, offsetBy: nInEach, limitedBy: endIndex) ?? endIndex
            result.append(transform(self[from ..< to]))
            from = to
        }
        return result
    }
}

let iarr = [1, 2, 3, 4, 5, 6, 7]
let sliceSums = iarr.eachSlice(3) { $0.reduce(0, +) }
print(sliceSums) // [6, 15, 7]